Re: [PATCH v2 22/28] memcg,list_lru: duplicate LRUs upon kmemcg creation

[Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

(2013/03/29 18:14), Glauber Costa wrote:
> When a new memcg is created, we need to open up room for its descriptors
> in all of the list_lrus that are marked per-memcg. The process is quite
> similar to the one we are using for the kmem caches: we initialize the
> new structures in an array indexed by kmemcg_id, and grow the array if
> needed. Key data like the size of the array will be shared between the
> kmem cache code and the list_lru code (they basically describe the same
> thing)
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> Cc: Dave Chinner <dchinner@redhat.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>   include/linux/list_lru.h   |  37 ++++++++++-
>   include/linux/memcontrol.h |  12 ++++
>   lib/list_lru.c             | 101 +++++++++++++++++++++++++++---
>   mm/memcontrol.c            | 151 +++++++++++++++++++++++++++++++++++++++++++--
>   mm/slab_common.c           |   1 -
>   5 files changed, 285 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> index 02796da..d6cf126 100644
> --- a/include/linux/list_lru.h
> +++ b/include/linux/list_lru.h
> @@ -16,12 +16,47 @@ struct list_lru_node {
>   	long			nr_items;
>   } ____cacheline_aligned_in_smp;
>   
> +/*
> + * This is supposed to be M x N matrix, where M is kmem-limited memcg,
> + * and N is the number of nodes.
> + */

Could you add a comment that M can be changed and the array can be resized.

> +struct list_lru_array {
> +	struct list_lru_node node[1];
> +};
> +
>   struct list_lru {
>   	struct list_lru_node	node[MAX_NUMNODES];
>   	nodemask_t		active_nodes;
> +#ifdef CONFIG_MEMCG_KMEM
> +	struct list_head	lrus;
> +	struct list_lru_array	**memcg_lrus;
> +#endif

please add comments, for what ....

>   };


>   
> -int list_lru_init(struct list_lru *lru);
> +struct mem_cgroup;
> +#ifdef CONFIG_MEMCG_KMEM
> +struct list_lru_array *lru_alloc_array(void);
> +int memcg_update_all_lrus(unsigned long num);
> +void list_lru_destroy(struct list_lru *lru);
> +void list_lru_destroy_memcg(struct mem_cgroup *memcg);
> +int __memcg_init_lru(struct list_lru *lru);
> +#else
> +static inline void list_lru_destroy(struct list_lru *lru)
> +{
> +}
> +#endif
> +
> +int __list_lru_init(struct list_lru *lru, bool memcg_enabled);
> +static inline int list_lru_init(struct list_lru *lru)
> +{
> +	return __list_lru_init(lru, false);
> +}
> +
> +static inline int list_lru_init_memcg(struct list_lru *lru)
> +{
> +	return __list_lru_init(lru, true);
> +}
> +
>   int list_lru_add(struct list_lru *lru, struct list_head *item);
>   int list_lru_del(struct list_lru *lru, struct list_head *item);
>   long list_lru_count_nodemask(struct list_lru *lru, nodemask_t *nodes_to_count);
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 4c24249..ee3199d 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -23,6 +23,7 @@
>   #include <linux/vm_event_item.h>
>   #include <linux/hardirq.h>
>   #include <linux/jump_label.h>
> +#include <linux/list_lru.h>
>   
>   struct mem_cgroup;
>   struct page_cgroup;
> @@ -469,6 +470,12 @@ void memcg_update_array_size(int num_groups);
>   struct kmem_cache *
>   __memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp);
>   
> +int memcg_new_lru(struct list_lru *lru);
> +int memcg_init_lru(struct list_lru *lru);
> +
> +int memcg_kmem_update_lru_size(struct list_lru *lru, int num_groups,
> +			       bool new_lru);
> +
>   void mem_cgroup_destroy_cache(struct kmem_cache *cachep);
>   void kmem_cache_destroy_memcg_children(struct kmem_cache *s);
>   
> @@ -632,6 +639,11 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
>   static inline void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
>   {
>   }
> +
> +static inline int memcg_init_lru(struct list_lru *lru)
> +{
> +	return 0;
> +}
>   #endif /* CONFIG_MEMCG_KMEM */
>   #endif /* _LINUX_MEMCONTROL_H */
>   
> diff --git a/lib/list_lru.c b/lib/list_lru.c
> index 0f08ed6..a9616a0 100644
> --- a/lib/list_lru.c
> +++ b/lib/list_lru.c
> @@ -8,6 +8,7 @@
>   #include <linux/module.h>
>   #include <linux/mm.h>
>   #include <linux/list_lru.h>
> +#include <linux/memcontrol.h>
>   
>   int
>   list_lru_add(
> @@ -184,18 +185,100 @@ list_lru_dispose_all(
>   	return total;
>   }
>   
> -int
> -list_lru_init(
> -	struct list_lru	*lru)
> +/*
> + * This protects the list of all LRU in the system. One only needs
> + * to take when registering an LRU, or when duplicating the list of lrus.
> + * Transversing an LRU can and should be done outside the lock
> + */
> +static DEFINE_MUTEX(all_memcg_lrus_mutex);
> +static LIST_HEAD(all_memcg_lrus);
> +
> +static void list_lru_init_one(struct list_lru_node *lru)
>   {
> +	spin_lock_init(&lru->lock);
> +	INIT_LIST_HEAD(&lru->list);
> +	lru->nr_items = 0;
> +}
> +
> +struct list_lru_array *lru_alloc_array(void)
> +{
> +	struct list_lru_array *lru_array;
>   	int i;
>   
> -	nodes_clear(lru->active_nodes);
> -	for (i = 0; i < MAX_NUMNODES; i++) {
> -		spin_lock_init(&lru->node[i].lock);
> -		INIT_LIST_HEAD(&lru->node[i].list);
> -		lru->node[i].nr_items = 0;
> +	lru_array = kzalloc(nr_node_ids * sizeof(struct list_lru_node),
> +				GFP_KERNEL);

A nitpick...you can use kmalloc() here. All field will be overwritten.

> +	if (!lru_array)
> +		return NULL;
> +
> +	for (i = 0; i < nr_node_ids ; i++)
> +		list_lru_init_one(&lru_array->node[i]);
> +
> +	return lru_array;
> +}
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +int __memcg_init_lru(struct list_lru *lru)
> +{
> +	int ret;
> +
> +	INIT_LIST_HEAD(&lru->lrus);
> +	mutex_lock(&all_memcg_lrus_mutex);
> +	list_add(&lru->lrus, &all_memcg_lrus);
> +	ret = memcg_new_lru(lru);
> +	mutex_unlock(&all_memcg_lrus_mutex);
> +	return ret;
> +}

returns 0 at success ? what kind of error can be shown here ?


> +
> +int memcg_update_all_lrus(unsigned long num)
> +{
> +	int ret = 0;
> +	struct list_lru *lru;
> +
> +	mutex_lock(&all_memcg_lrus_mutex);
> +	list_for_each_entry(lru, &all_memcg_lrus, lrus) {
> +		ret = memcg_kmem_update_lru_size(lru, num, false);
> +		if (ret)
> +			goto out;
> +	}
> +out:
> +	mutex_unlock(&all_memcg_lrus_mutex);
> +	return ret;
> +}




> +
> +void list_lru_destroy(struct list_lru *lru)
> +{
> +	if (!lru->memcg_lrus)
> +		return;
> +
> +	mutex_lock(&all_memcg_lrus_mutex);
> +	list_del(&lru->lrus);
> +	mutex_unlock(&all_memcg_lrus_mutex);
> +}
> +
> +void list_lru_destroy_memcg(struct mem_cgroup *memcg)
> +{
> +	struct list_lru *lru;
> +	mutex_lock(&all_memcg_lrus_mutex);
> +	list_for_each_entry(lru, &all_memcg_lrus, lrus) {
> +		kfree(lru->memcg_lrus[memcg_cache_id(memcg)]);
> +		lru->memcg_lrus[memcg_cache_id(memcg)] = NULL;
> +		/* everybody must beaware that this memcg is no longer valid */
> +		wmb();
>   	}
> +	mutex_unlock(&all_memcg_lrus_mutex);
> +}
> +#endif
> +
> +int __list_lru_init(struct list_lru *lru, bool memcg_enabled)
> +{
> +	int i;
> +
> +	nodes_clear(lru->active_nodes);
> +	for (i = 0; i < MAX_NUMNODES; i++)
> +		list_lru_init_one(&lru->node[i]);
> +
> +	if (memcg_enabled)
> +		return memcg_init_lru(lru);
>   	return 0;
>   }

> -EXPORT_SYMBOL_GPL(list_lru_init);
> +EXPORT_SYMBOL_GPL(__list_lru_init);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ecdae39..c6c90d8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2988,16 +2988,30 @@ int memcg_update_cache_sizes(struct mem_cgroup *memcg)
>   	memcg_kmem_set_activated(memcg);
>   
>   	ret = memcg_update_all_caches(num+1);
> -	if (ret) {
> -		ida_simple_remove(&kmem_limited_groups, num);
> -		memcg_kmem_clear_activated(memcg);
> -		return ret;
> -	}
> +	if (ret)
> +		goto out;
> +
> +	/*
> +	 * We should make sure that the array size is not updated until we are
> +	 * done; otherwise we have no easy way to know whether or not we should
> +	 * grow the array.
> +	 */
> +	ret = memcg_update_all_lrus(num + 1);
> +	if (ret)
> +		goto out;
>   
>   	memcg->kmemcg_id = num;
> +
> +	memcg_update_array_size(num + 1);
> +
>   	INIT_LIST_HEAD(&memcg->memcg_slab_caches);
>   	mutex_init(&memcg->slab_caches_mutex);
> +
>   	return 0;
> +out:
> +	ida_simple_remove(&kmem_limited_groups, num);
> +	memcg_kmem_clear_activated(memcg);
> +	return ret;

When this failure can happens ? This happens only when the user
tries to set kmem_limit and doesn't affect kernel internal logic ?

Thanks,
-Kame

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